The purpose of this project is to assess the relative contributions of genetic and environmental factors to alcohol drinking and response to alcohol challenge. The project is composed of three studies. In the first, male monozygotic (MZ) and dizygotic (DZ) twin pairs complete a 28- day genetic and environmental factors to frequency, amount, and pattern of alcohol consumption. In addition, self-reports of contact between cotwins will permit estimation of the importance of shared environment on cotwin similarities in alcohol drinking. In a second study, electrophysiological and behavioral measures are being employed in a study of drug response. Adult males are tested in two separate sessions using a protocol which consists of electrophysiological measures (e.g., brainstem auditory evoked responses, spectrally analyzed EEG, and visual and auditory event-related potentials), a behavioral measure of attention, self-reports of affect, and a measure of standing stability. Following baseline recording, subjects are administered 0.80 g/kg of 95% ethyl alcohol. This study will permit estimation of the retest stability of the alcohol effects. This information will be critical in the dose-response analysis and in the selection of table measures for a twin study. In a third study, male MZ and DZ twin pairs receive, in three separate testing sessions, a placebo and two doses of alcohol (0.40 and 0.80 g/kg). The use of placebo and multiple doses of alcohol will permit conclusions about the effects of alcohol on information processing, response produced, and motor activity. The protocol will be similar to that used in the study described above. The twin design will provide information on the relative contributions of genetic and environmental factors to variability in these measures in the drug-free state and following response to alcohol challenge.